Electric control circuit



March 5, 1963 G. M. HIPPLE 8 ELECTRIC CONTROL CIRCUITv Original Filed Feb. 23, 1956 20 44 mags) a 5| l u: D A

} F IDROP :our 0 R R R RESISTANCE INVENTOR. GEORGE M HIPPLE .Fig- E" AGENT 3,680,568 ELECTREQ CGNTRQL ClRCUl'l George M. Hippie, Columbus, Ohio, assignor to American Braire Shoe Qompany, New York, NY, a corporation of Delaware Original application Feb. 23, 1956, Ser. No. 567,255, now Patent No. 2,945,990, dated July 19, 1960. Divided and this application Apr. 7, 195%, Ser. No. 726,985

Claims. (Cl. 317-435) This invention relates to electric apparatus and more particularly to an electric circuit or system adapted to control any solenoid actuated or operated device and which circuit or system may be employed with particular advantage, for example, for controlling the operation of a hydraulic press.

The main object of this invention is to provide an improved electric circuit which includes two switches both of which must be closed to initiate the operation of an operating solenoid and in which, after said operation is initiated, only one of said switches need be maintained closed to maintain said solenoid in operation.

Another object of the invention is to provide an improved electric circuit as set forth in the foregoing object which may be used with particular advantage in controlling the hydraulic apparatus, and consequently the operation, of a hydraulic press in which the press operator must use both of his hands to operate the mentioned switches to initiate operation of the press and after said operation is initiated the operator may release one of said switches and the pressing operation of the press will continue.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred form of embodiment of the invention is clearly shown.

In the accompanying drawings:

' FIG. 1 is a diagrammatic showing of an electric control circuit including features of the invention, said circuit being shown associated with the hydraulic system of a hydraulic press which it controls, and

FIG. 2 is a graph showing current characteristics of a solenoid operating on alternating current and connected in series with a resistance.

This application is a division of my copending application Serial No. 567,256, filed February 23, 1956, for an Electric Control Circuit, now Patent No. 2,945,990.

FIG. 1 of the drawings illustrates an electric control circuit or system 265 associated with the hydraulic apparatus or system 21 of a hydraulic press whi h is indicated generally at 22. The hydraulic system 21 per se is the invention of Robert Smilges and is fully described and claimed in his copending application Serial No. 559,438, filed lanuary 16, 1956, for Hydraulic Press and Control Means, now Patent No. 2,927,55 8. This system is made a part of this application for illustrating the operation and purpose of the present invention and it is described herein only in suificient detail to set forth the operation of the apparatus herein claimed. For an understanding of the details and operation of the hydraulic system, reference should be had to the above identified application to Robert Smilges.

Referring more particularly to FIG. 1 of the drawings, the hydraulic press 22 is shown as being comprised of a bed 23 and rant 24. Ram 24- is shown as forming the piston rod of a double-acting reciprocating hydraulic motor which includes a cylinder 25 and a piston 26. The hydraulic system 21, in addition to the press motor, also includes a pump 27 which is driven by an electric motor 28 through sheaves and a belt 29, a reservoir or tank 31) for hydraulic liquid used in the system, a hydraulic control valve 31 and suitable conductors or pipes which are 3,0805% Patented ll/lar. 5, 1963 fully indicated in the drawing. The parts of the above described structure are shown in the drawings in the positions in which they occupy when the ram is held in its up position. Before describing the operation of the hydraulic system further, it should be pointed out that the pump 27 has two separate high pressure outlet or output ports which are connected respectively to conduits or lines 32 and 33 formed in the body 34 of valve 31 and that the volume of liquid delivered to the lines 32 and 33 are preferably, but not necessarily, difierent.

When the parts of the control valve 31 are in the positions shown in the drawings and the ram 34 is held in its up" position, hydraulic liquid flows from the tank 30 to the inlet port of pump 27 in which it is divided and caused to fiow to lines 32 and 33 as aforesaid. Liquid from the low volume output port of pump 27 flows through line 32 to a groove in a sleeve 35 in valve body 34 and from this groove 34 it passes to the interior of the sleeve 35 and to the upper end of a spool 36 and also to a conduit 37 in valve body 34 which is adapted to be closed by a solenoid operated valve 38. The construction of the control valve 31 is such that until the valve 38 is closed the spool 36 will remain in the position shown and the combined output volumes of the pump 27 will be directed through a conduit 3% to the bottom of the cylinder 25 and piston 26 to urge the latter to its up position. This liquid will be returned from the top of cylinder 25 through a conduit 40 to valve 31 and tank 30. Upon the closing of the valve 38, hydraulic pressure will increase above the spool 36 and shift it downwardly to close a valve 41 which is connected in series with the valve 38. After valve 4-1 is closed, it valve 38 is opened, the valve 31 will cause liquid to be delivered to the press motor to complete automatically one cycle of operation of the press, and all of the parts, after the completion of said one cycle, will return to the positions shown in the drawing. If the valve 38 is not open, the ram 24 will travel toward the bed 23, or work thereon, and will remain in an extended position until valve 38 is opened.

The electric circuit or system 29 controls the operation of the hydraulic system 21 and it includes a solenoid 42 having a winding 43 for operating the valve 38 of said hydraulic system 21. One side of the solenoid coil or winding 4-3 receives electric current directly from a main lead line 44 and the other side 45 of coil or winding 33 is connected through a pair of resistors 46 and i7 in series to the other main lead line 48. Resistors 46 and 47 are such that when they are connected in series, as above described, insufiicient current will fiow through them to energize the solenoid coil 43 sufiiciently to move the solenoid armature or core to its operated position, that is, insufiicient current will flow through the coil 43 to operate solenoid 42. The end 45 of coil or winding 43 may also be connected directly to lead line 48 through a pair of normally open push type switches 4d and connected in series or through either of resistors 46 and 47 and one of switches 4? and 5t, and a bypass conductor or line 51 connected from between the switches 49 and 56 to between the resistors 46 and 47.

In the operation of the circuit or system, in order to energize the solenoid id to operate it initially, it is necessary to close both push type switches 49 and 50 at the same time, but not necessarily simultaneously, in order to bypass both of the resistors 46 and 47 and to permit the full line current from lines 44 and 4-8 to flow to the coil or winding 43. After the solenoid 4 2 has been energized initially by said flow of current either of the push type switches 49 or St? may be opened and the solenoid 42 will remain in operation. Stated another way, when the circuit is employed in connection with the hydraulic system 21 it is necessary to close both push type switches s9 and 5th to close valve 33 and after said valve 38 is closed 3 7 only one of'said switches 49or 50 need be maintained closed to hold the valve 38 closed.

'it will be seen that after the initial operation of solenoid 42 that if switch 49 is permitted to open that the low of current to coil '43 from lead line 48 will be through closed switch 59 bypass connector 51 and resistor 4 6 to side 45 of the coil 43. It will also be seen that irswitch 50 is opened that the flow of current to coil 43 from lead line 948 will 'be through'resistor 47, bypass connector 51 and switch49 to side 45 of coil 43. Thus when both switches 49 and 5d areclosed, both resistors 46 and 47 will be bypassed. When switch 49 is opened and switch 50 is closed, resistor 4'7 will be bypassed and whenswitch St is openedand switch 49 is closed resistor 46 will be bypassed.

FIG. 2 is a graph showing current characteristics of a solenoid operating on alternating current which are taken advantage of in the circuit seen in the drawingsL In this. graph, current flowing through the coil or 'winding'of the solenoid is represented as a function of a'resi'st'ance' connected in series with the solenoid. I

Referring more particularly to the graph shown in FIG. 2, R represents a resistance which will permitno current to flow through a solenoid coil and-as 'R is decreased progressively (moved toward point the current which flows through the solenoid coil will increase,

as indicated by the line A, up to the point B where the solenoid picks up and operates by shifting its core. When the current flowing in the solenoid coilincreases to the pick up point B and the solenoid operates, the cur-. rent flowing through the solenoid coil drops immediately to the point C due to the increase in impedance of the solenoid and as the resistance R- isfurther decreased the current flowing through the solenoid coil will increase along line D up to the point B of maximum current applied to it.

When the resistance R is increased from the point 0 of no resistance, the current flowing through the solenoid coil decreases along line D to a drop out point F at which the magnetic field crested by the coil of the solenoid is insuflicient to maintain the solenoid in operation. Upon shifting of the solenoid core at the drop out point P, current flowing through the coil will rise immediately along the line G to line A due to the decrease in impedance of the solenoid and will then continue to decrease along line A as the resistance is increased.

As indicated by the graph, less. resistance is required to cause the solenoid to pick up or operate to shift its core than is required to permit the solenoid to drop out. Stated another way, it requires more current flowing through the solenoidcoil to energize the solenoid sufliciently to cause it to operate than it requires to keep it in operation once it has been initially energized and operated.

In the electric circuit or system, each of the resistances 4.6 and 47 is such as to offer resistance to current (which could. be shown on the graph as lying at a point between R-1 and R-2) so that when either of the resistances is connected in series with the coil or winding 43 of solenoid 42 suflicient current will be applied to the coil 43 to maintain the solenoid 42 in operation once it has beeninitially energized by closing both push type switchcs-49 and t? .and so that when the resistors 46 or 47 are connected in :series, as when both switches 49 and 5d are opened, the combined resistance of the resistors 46 and 47 will-besuch as to cause the current applied to the coil 43 to be in suificient to maintain the solenoid in operation (the combined resistances of resistors 46 and47 would fall upon the graph somewhere between the point R-1 and R).

The hydraulic press 22 including the hydraulic apparatus-or system 21 performs each cycle of operation very rapidly, that is, when valve 38 is closed the ram 24 travels toward the bed, or work on the bed, or returns to its up position rapidly and at such a rate of speed that an operatorhas not timeto release either of the push type switches 49 or 50 and get either of his hands caught under 4 the ram. He may, however, release or permit either or both of these switches to open while the ram istraveling toward the press bed 23 or work thereon and should he permit only one of said switches to open the ram will travel only to its extended position and dwell at a maximum pressing pressure upon work on the bed 23.

For the reasons set forth, it will be seen that the operator can not cheat the system in operating the press as by blocking one of the push type switches in a closed position since both of said-switches 49 and 5d must be opened to cause the ram to return from its dwell position to its up position. a

While the form of embodiment of the present invention as herein disclosed constitutes a preferred form, it is to be understood that other forms mig-ht be adopted, all coming within-thescope'of the'clai'ms which follow,

I claims 1, In a cannot circuit for a hydraulic press-having a valve hot-"controlling the operation of said press solenoid means'including winding means for controlling the opera-' tion of said valve, conductor me'ahs for conducting electric current to said winding inean s, -a pair of resistor means iii-said conductor means, apair of switches, and meansconnecting said switches each to lay-pass one of said resistormeans whereby closing of both of said switches will by pass both of saidresistor means to pass electric current to said winding means suflicient to initiate operation of said solenoid and thereafter only one of said switches need be maintained closed to pass suflicient current to said winding means to maintain said solenoid in operation.

2. A -safety' -controlcircuit for a cyclically operable device including a solenoid which mus-t initially be pulled in, then dropped out and subsequently pulled in to cause a recycling of said'device, said solenoid having solenoid winding means, conductor meansior conducting electric current to said winding means, a pair of resistor means in said conductor means, a pair-of switches, and' m'eans connecting one of said switches'across'one of said resistor means and the other of said switches across the other of said resistor means, whereby when both or" said switches are closed current flowing in said conductor means by-passes both of'said resistor means and whereby when only oneof said switches is closed current flowing in said conductor means lay-passes only one of said resistor means, said resistor means being related't-o said solenoid winding means, whereby said solenoid is pulled in only when both switches are closed and said solenoid is dropped out only when both switches are opened.

3. A safety control circuit for a cyclically operable device including a solenoid which must initially be pulled in, then dropped out and subsequently pulled in to cause a a recycling of said device, said solenoid having solenoid winding meansfconductor means for conducting electric current to said win-ding means, a pair of resistor means in said conductor means, a pair of manually operated switches, and means connecting one of saidswitches across one of said resistor means and the'other of said switches across the other of said resistor means, whereby when both of said switches are closed current ilowin-g'in said conductor means by-passes both'of said resistor means and where-by when only one of said switches is closed current flowing in said conductor means Toy-passes only one of said' resistor means, saidresistor means being related to said solenoid winding means whereby said solenoid is pulled in only when both switches are closed and said solenoid is dropped out only when both switches are opened.

4. A safety control circuit for a cyclically operable device including a solenoid which must initially be pulled in, then dropped out and subsequently pulled in to cause a recycling of said device, said solenoid having solenoid winding means, conductor means for conducting electric current to said winding means, a pair of resistor means in said conductor means, a pair of switches, and means connectingsaid switches each to by-pass one of said resistor 5 means whereby closing of both of said switches will bypass both of said resistor means to pass electric current to said winding means sufficient to initiate operation of said solenoid and thereafter only one of said switches need be maintained closed to pass sufiicient current to said winding means to maintain said solenoid in operation.

5. A safety control circuit for a cyclically operable de vice including a solenoid which must initially be pulled in, then dropped out and subsequently pulled in to cause a recycling of said device, said solenoid having solenoid winding means, conductor means for conducting electric current to said winding, a pair of series connected resistor means in said conductor means, a pair of normally open manually operated switches, means connecting said switches in series relation across said pair of resistor means, and means connecting each of said switches across one of said resistor means whereby when both of said switches are closed current flowing in said conductor means by-passes said resistor means and whereby when one only of said switches is closed current flowing in said conductor means by-passes only one of said resistor means, said resistor means being related to said solenoid winding means whereby said solenoid is pulled in only when both switches are closed and said solenoid is dropped out only when both switches are opened.

References Cited in the file of this patent UNITED STATES PATENTS 2,257,361 Yorkey Sept. 30, 1941 2,404,980 Munschauer July 30, 1946 2,535,785 Couri Dec. 26, 1950 2,579,595 McLane Dec. 25, 1951 FOREIGN PATENTS 593,601 Great Britain Oct. 21, 1947 

1. IN A CONTROL CIRCUIT FOR A HYDRAULIC PRESS HAVING A VALVE FOR CONTROLLING THE OPERATION OF SAID PRESS, SOLENOID MEANS INCLUDING WINDING MEANS FOR CONTROLLING THE OPERATION OF SAID VALVE, CONDUCTOR MEANS FOR CONDUCTING ELECTRIC CURRENT TO SAID WINDING MEANS, A PAIR OF RESISTOR MEANS IN SAID CONDUCTOR MEANS, A PAIR OF SWITCHES, AND MEANS CONNECTING SAID SWITCHES EACH TO BY-PASS ONE OF SAID RESISTOR MEANS WHEREBY CLOSING OF BOTH OF SAID SWITCHES WILL BY-PASS BOTH OF SAID RESISTOR MEANS TO PASS ELECTRIC CURRENT TO SAID WINDING MEANS SUFFICIENT TO INITIATE OPERATION OF SAID SOLENOID AND THEREAFTER ONLY ONE OF SAID SWITCHES NEED BE MAINTAINED CLOSED TO PASS SUFFICIENT CURRENT TO SAID WINDING MEANS TO MAINTAIN SAID SOLENOID IN OPERATION. 